Climate Change and Corals: Laying Siege to the Adaptation Mythos

This is my rebuttal to the recent blog by Jacob Jerome a Graduate Student and Intern at the University of Miami in the RJ Dunlap Marine Conservation Program titled “Climate Change and Corals: is it too late?”

Dear Mr. Jerome,

While I’m envious of your glass half-full outlook on the fate of corals to global warming, I feel that your only helping to propagate a persistent mirage; namely that *all* coral individuals or communities will adaptively respond in time to thermal stress. As will be argued here, this removes the onus of implementing a global strategy that can reduce both local and global stresses and implies that we have more time with respect to the pressures on coral reefs and related ecosystems.

Climate change is a major threat with rising sea surface temperatures and ocean acidification acting as chronic stresses which operate over long timescale. Implications include many adverse effects, bleaching, reduced growth and reproductive outputs, death and loss of biodiversity (Loya et al., 2001; Fabricius, 2005; De’ath et al., 2012). Thermal stress could potentially also increase viral load and corals susceptibility to disease. If we stopped emissions today, much of the warming would persist for centuries after greenhouse gas emissions stopped. If the current rate of emissions holds (business-as-usual), or increases, the ability of corals to respond evolutionarily to the rapid pace of change is doubtful (Dove et al., 2013).

Although evolutionary history is complicated by cyclical climate changes over geologic time (Vernon, 2000), coral reef system have changed as a result of climate change with few contemporary reefs existing in a “pristine” state. Most long-term studies show declines of around 50% since the early 1980’s. During this period coral composition has changed with the dominance of species being altered as well. By comparing recent events of decline to those of the past indicate that current rates of changes are orders of magnitude higher than they have been for tens of millions of years. You mentioned in your article that according to the Status of Coral Reefs of the World: 2008, 15 percent are seriously threatened. However, more recent studies looking across the world’s coral reefs, 75% are threatened (Burke et al., 2011). I’m not of the “coral reefs are doomed” prophecy point of view but I do believe that the situation is dire and that returning reefs to a pristine condition is not a realistic goal. Although I’m not suggesting we abandon all hope and toss in the towel (after all I’m not entirely a curmudgeon because then why would I even bother with the work I do?), I just think we need to be careful, and to tread lightly, when communicating as major funding agencies are often evaluating whether or not to continue funding coral reef management and management-related research.

Studies documenting recovery have yielded mixed conclusions. Some authors have proposed that individuals, or indeed communities, can adaptively respond to thermal stress (Logan et al., 2014). However; the broader scientific community has concerns as to whether Scleractinian (reef building species) will survive global warming and ocean acidification (Baker et al., 2008; Vernon et al., 2009; Hoegh-Guldberg, 2014). I think this is especially important for blog posts which are aimed at the broader public. We need to be clear about internal disagreement within the ivory towers for such contentious, and politically sensitive topics such as climate change. This has played out vividly in the past in such instances as “climategate”. As scientists we should leave ample room in our communications to highlight the dissent and nuances to complex topics in a way that the general public will recognize and think critically about.

I felt that you spun a one-sided story, in that you only included the exceptions to the rule rather than covering the wider accepted literature on reef resilience and adaptability. Most studies incorrectly extend the evidence which is necessary but not sufficient to support the conclusions that coral reefs will survive due to their ability to acclimatise, adapt and/or migrate to the current rapid environmental changes (Hoegh-Guldberg, 2014).

A couple of points I would like to address critically are as followed:

  • You mentioned the study by Raina and colleagues (2013) and suggested that this was evidence that this is a “fight” against temperature shifts? I fail to see how you can jump to such conclusions when juvenile corals were only exposed to elevated temperatures for 12 days. Moreover, adult colonies of A. millepora exposed to 32°C for 10 days had an 84% reduction in their Symbiodinium. To me, there findings only suggest a stress response which likely plays some role as an anti-oxidant in cellular processes. The loss of biodiversity in coral and symbiodinium following bleaching, added to increased probability of consecutive bleaching would suggest a loss in reef cover and diversity if current trends continue (Stat et al., 2006). The authors posit that release of DMS, as a result of bacterial conversion of DMSP, could be a major source of cloud condensation nuclei. However, I feel that your readiness to extrapolate and say that it would offer some sort of adaptive advantage is a far-reach by any estimate. Especially since the authors acknowledge that the declining trend in coral cover due to anthropogenic stressors can further destabilize local climate regulation.
  • Second, you mention the Cayman island recovery in 7 years as investigated by Manfrino et al. (2013). While I appreciate seeing findings which are contrary to common assumptions I think we need to take them with a large grain of salt. I would be the first to point out that in Samoa corals can thrive in 35°C water for a few hours each day, a “fact that they’re there means they’ve adapted to survive says Steve Palumbi. However, I believe this is an isolated case, and therefore not representative of the coral reefs by-and-large. Similar statistics have engendered debates about the value of marine protected areas (Huntington et al., 2011). We need to be honest by not omitting inconvenient truths, this is what it means to be a scientist, instead of say a lobbyist or philosopher. Johnson and Saunders (2014) suggest that demographic and economic factors influence the psychology of human decision to such a degree that it has a major impact on local ecology. The work they did in Curacao and Bonaire showed that socio-cultural-economic backgrounds influence marine resource management approaches which likely has an effect on the local ecosystems resilience and recovery. Curacao’s economy primarily relies on fishing (making money by exploiting resources), whereas Bonaire’s economy relies more heavily on revenue from tourism (making money by preserving resources). The Cayman Islands are therefore not representative of the vast majority of countries which harbor coral reefs (and rely on a subsistence economy) and it is unlikely that this study is representative of the broader global coral reef ecosystem.
  • Thirdly, you believe that “new scientific research indicates that not all corals are quite ready to give up”. I agree with you to the extent that this is true as in the case of Samoan corals or Dubai in the Arabian Gulf. Nonetheless, at what cost to the ecosystem if only a few corals, or communities, can survive? Massive plating and encrusting morphologies have been shown to be less susceptible than branching morphologies in a broad range of habitats, biogeographic regions and sea warming events (Loya et al., 2001). It has been shown that the rugosity of the substratum is positively correlated with observed fish species richness in most reports (Gratwicke & Speight, 2005) so a loss of substrate complexity could be bad news in a warming world.

One more thing to consider is symbiodinium clade changes, as algal symbionts are thought to play a key role in coral resistance and resilience. At the risk of not keeping my rebuttal germane (I know you never mentioned this, likely for the obvious reasons I’m about to bring up) I should mention another contentious issue as it relates to adaptation. Its alluring to think that hosts may switch/shuffle symbionts (Buddemeier & Fautin, 1993) for ones that may be more tolerant to the changing environmental conditions; this would overcome the slow pace of coral host evolution (a consequence of long generation times and low population diversity due to asexual reproduction). However, Lewis and Coffroth (2004) have shown that the octocoral Briareum only takes up symbionts that are found in normal conditions which does not represent the uptake of completely new symbionts to that host species. This suggest that the adaptive potential of corals may be limited to the existing types of symbionts present in the host. A number of authors have presented convincing data which suggests that few hosts have more than one type of symbiont (Baird et al., 2007), generalist corals such as Acropora and Pocillopora have a high flexibility, while specifist corals such as Porites have a low flexibility to symbionts diversity. Moreover, corals which harbor clade D are more thermo-tolerant, but the coral fitness may suffer energetic costs such as a reduction of growth and reproduction (Jones & Berkelmans, 2011). I think the paucity of evidence of propitious effects such as coevolution in the literature requires further investigation.

Due to the large policy implications I feel that your post should set a higher standard of demonstrating results beyond a reasonable doubt, or at the very least recognizing that scientists are split over this issue. I’m worried that certain subsets of the public will cherry pick results and trumpet “scientists prove reef extinction is not occurring”. After all there are those with a vested interest who will pervert fact and take things out of context. Others, such are media reporting may just skim right over this and not do background research on the actual papers referenced. In my own humble opinion the belief that somehow corals will magically evolve into a resilience state and alter the current trajectory of coral reef ecosystems under rapid anthropogenic climate change is a dangerous pipe-dream indeed.

References:

Baird, A.H., Cumbo, V.R., Leggat, W., Rodriguez-Lanetty, M. (2007) Fidelity and flexibility in coral symbioses. Marine Ecology Progress Series 347:307-309

Baker, A.C., Glynn, P.W., Riegl, B. (2008) Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuarine, Coastal and Shelf Science 80(4):435-471.

Buddemeier, R.W. & Faustin, D.G. (1993) Coral bleaching as an adaptive mechanism: a testable hypothesis. Bioscience 43:320-326.

Burke, L., Reytar, K., Spalding, M., Perry, A. (2011) Reefs at Risk Revisited. Washington, DC: World Resources Institute.

De’ath, G., Fabricius, K.E., Sweatman, H., Puotinen, M. (2012) The 27-year decline of coral cover on the Great Barrier Reef and its causes. Proceedings of the National Academy of Sciences of the United States of America 109(44): 17995-17999.

Dove, S.G., Kline, D.I., Pantos, O., Angly, F.E., Tyson, G.W., Hoegh-Guldberg, O. (2013) Future reef decalicification under a business-as-usual C02 emission scenario. PNAS 110(38):15342-15347.

Fabricius, K. E. (2005) Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis. Marine Pollution Bulletin 50(2):125-146.

Gratwicke, B., Speight, M.R. (2005) The relationship between fish species richness, abundance and habitat complexity in a range of shallow tropical marine habitats. Journal of Fish Biology 66:650-667.

Hoegh-Guldberg, O., 2004. Coral reefs in a century of rapid environmental change. Symbiosis 37:1–31.

Hoegh-Guldberg, O. (2014) Coral reef sustainability through adaptation: glimmer of hope or persistent mirage? Current opinion in Environmental Sustainability. 7:127-133.

Huntington BE, Karnauskas M, Lirman D (2011) Corals fail to recover at a Caribbean marine reserve despite ten years of reserve designation. Coral Reefs 30:1077–1085.

Johnson, A.E. and Saunder, D.K. (2014) Time preferences and the management of coral reef fisheries. Ecological Economics 100:130-139.

Jones, A.M., and Berkelmans, R. (2011) Tradeoffs to thermal acclimation: energetics and reproduction of a reef coral with heat tolerant Symbiodinium type-D. Journal of Marine Biology 2011:1-12.

Lewis, C.L., Coffroth, M.A. (2004) The acquisition of exogenous algal symbionts by an octocoral after bleaching. Science 304:1490–1492.

Logan, C.A., Dunne, J.P., Eakin, C.M., Donner, S.D. (2014) Incorporating adaptive responses into future projections of coral bleaching. Global Change Biology 20:125-139.

Loya, Y., Sakai, K., Yamazato, K., Nakano, Y., Sambali, H., Van Woesik, R. (2001) Coral bleaching: the winners and the losers. Ecology Letters 4(2): 122-131.

Manfrino, C., Jacoby, C.A., Camp, E., Frazer, T.K. (2013) A Positive Trajectory for Corals at Little Cayman Island. PLoS ONE 8(10):e75432.

Raina, J.B., Tapiolas, D.M., Forêt, S., Lutz, A., Abrego, D., Ceh, J., Seneca, F.O., Clode, P.L., Bourne, D.G. Willis, B.L., Motti, C.L. (2013) DMSP biosynthesis by an animal and its role in coral thermal stress response. Nature Letters, 502: 677-680.

Stat, M., Carter, D., Hoegh-Guldberg, O. (2006). The evolutionary history of Symbiodinium and scleractinian hosts – Symbiosis, diversity, and the effect of climate change. Perspectives in Plant Ecology, Evolution and Systematics 8:23-43.

Vernon, J. (2000) Corals of the World. Australian Institute of Marine Science, Townsville.

Veron, J.E.N., Hoegh-Guldberg, O., Lenton, T.M., Lough, J.M., Obura, D.O., Pearce-Kelly, P., Sheppard, C.R.C., Spalding, M., Stafford-Smith, M.G., and Rogers, A.D. (2009) The coral reef crisis: The critical importance of <350 ppm CO2. Marine Pollution Bulletin 58(10):1428-1436.